Interconnect structures with intermetallic palladium joints and associated systems and methods

ABSTRACT

Interconnect structures with intermetallic palladium joints are disclosed herein. In one embodiment, a method of forming an interconnect structure includes depositing a first conductive material comprising nickel on a first conductive surface of a first die, and depositing a second conductive material comprising nickel on a second conductive surface of a second die spaced apart from the first surface. The method further includes depositing a third conductive material on the second conductive material, and thermally compressing tin/solder between the first and third conductive materials to form an intermetallic palladium joint that extends between the first conductive material and the second conductive material such that one end of the intermetallic palladium joint is bonded directly to the first conductive material and an opposite end of the intermetallic palladium joint is bonded directly to the second conductive material.

TECHNICAL FIELD

The disclosed embodiments relate to interconnect structures insemiconductor devices. In several embodiments, the present technologyrelates to interconnect structures with conductive joints, such as metalsolder joints.

BACKGROUND

Packaged semiconductor dies, including memory chips, microprocessorchips, and imager chips, typically include a semiconductor die mountedon a substrate and encased in a plastic protective covering. The dieincludes functional features, such as memory cells, processor circuits,and imager devices, as well as bond pads electrically connected to thefunctional features. The bond pads can be electrically connected toterminals outside the protective covering to allow the die to beconnected to higher level circuitry. Within some packages, semiconductordies can be stacked upon and electrically connected to one another byindividual interconnects placed between adjacent dies. In such packages,each interconnect can include a conductive material (e.g., solder) and apair of contacts on opposing surfaces of adjacent dies. For example, ametal solder can be placed between the contacts and then reflowed sothat it reacts with the metal at each of the contacts to form aconductive joint.

One challenge with traditional solder joints is that solder can migrateor spread during reflow. For example, the solder can be displaced whenit is squeezed between the metal contacts. Also, certain forces, such assurface tension, can cause the solder to wick away from a conductivesurface and onto other surfaces. One specific challenge occurs when thesolder wicks onto and forms an intermetallic material on the sidewallsof a metal contact. Such intermetallic materials on the sidewalls canultimately degrade the overall electrical and/or thermal conductively ofthe contact. For example, conventional tin/copper intermetallicmaterials can reduce the overall thermal conductivity of a copper-basedcontact. Further, in vertical interconnects (e.g., copper posts), thesolder can consume a substantial amount of metal, which can cause theinterconnect to slump and/or form voids in the sidewalls (e.g., due toKirkendall voiding).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a semiconductor device havinginterconnect structures in accordance with an embodiment of the presenttechnology.

FIG. 2 is an enlarged cross-sectional view showing an individualinterconnect structure in accordance with an embodiment of the presenttechnology.

FIGS. 3A-3G are cross-sectional views illustrating a semiconductordevice at various stages in a method for making interconnect structuresor other connectors in accordance with selected embodiments of thepresent technology.

FIGS. 4A and 4B are illustrations showing interconnect structures havingintermetallic palladium joints.

FIG. 5 is a schematic view of a system that includes a semiconductordevice in accordance with embodiments of the present technology.

DETAILED DESCRIPTION

Specific details of several embodiments of semiconductor deviceinterconnect structures having intermetallic palladium joints andassociated systems and methods are described below. The terms“semiconductor device” and “semiconductor die” generally refer to asolid-state device that includes semiconductor material, such as a logicdevice, memory device, or other semiconductor circuit, component, etc.Also, the terms “semiconductor device” and “semiconductor die” can referto a finished device or to an assembly or other structure at variousstages of processing before becoming a finished device. Depending uponthe context in which it is used, the term “substrate” can refer to awafer-level substrate or to a singulated, die-level substrate. A personskilled in the relevant art will recognize that suitable steps of themethods described herein can be performed at the wafer level or at thedie level. Furthermore, unless the context indicates otherwise,structures disclosed herein can be formed using conventionalsemiconductor-manufacturing techniques. Materials can be deposited, forexample, using chemical vapor deposition, physical vapor deposition,atomic layer deposition, spin coating, and/or other suitable techniques.Similarly, materials can be removed, for example, using plasma etching,wet etching, chemical-mechanical planarization, or other suitabletechniques. A person skilled in the relevant art will also understandthat the technology may have additional embodiments, and that thetechnology may be practiced without several of the details of theembodiments described below with reference to FIGS. 1A-5.

As used herein, the terms “vertical,” “lateral,” “upper,” and “lower”can refer to relative directions or positions of features in thesemiconductor device in view of the orientation shown in the Figures.For example, “upper” or “uppermost” can refer to a feature positionedcloser to the top of a page than another feature. These terms, however,should be construed broadly to include semiconductor devices havingother orientations, such as inverted or inclined orientations wheretop/bottom, over/under, above/below, up/down, and left/right can beinterchanged depending on the orientation.

FIG. 1 is a cross-sectional view of a semiconductor device 100 havinginterconnect structures 120 in accordance with an embodiment of thepresent technology. As shown, the semiconductor device 100 includes afirst semiconductor die 102 a and a second semiconductor die 102 b(collectively “semiconductor dies 102”) adjacent to the first die 102 a.In the illustrated embodiment of FIG. 1, the semiconductor device 100includes two semiconductor dies, although in practice the semiconductordevice 100 can include a different number of semiconductor dies, such asthree dies, four dies, eight dies, sixteen dies, or more. For example,in another embodiment, the semiconductor device can include a thirdsemiconductor die 102 c (shown in hidden lines) on the first die 102 a,and a fourth semiconductor die 102 d (shown in hidden lines) on thesecond die 102 b. Each of the semiconductor dies 102 includes integratedcircuitry 103, a substrate 106 (e.g., a silicon substrate), andthrough-substrate vias (TSVs) 110 extending through the substrate 106from a first side 108 a to a second side 108 b. The integrated circuitry103 can include, for example, a memory circuit (e.g., a dynamic randommemory (DRAM)), a controller circuit (e.g., a DRAM controller), a logiccircuit, and/or other circuits. In at least some embodiments, thesemiconductor device 100 can include other structures and features suchas a casing (e.g., a thermally conductive casing) that encloses thesemiconductor dies 102 within an enclosure; an interposer, a printedcircuit board, and/or another substrate carrying the semiconductor dies102; and/or an underfill material deposited or otherwise formed aroundand/or between the dies.

As further shown in FIG. 1, the interconnect structures 120 are disposedbetween the semiconductor dies 102. Each of the interconnect structures120 includes a first conductive element 122, a second conductive element123, and a conductive joint 125 coupling the first conductive element122 to the second conductive element 123. The individual secondconductive elements 123 are coupled to corresponding TSVs 110 at thesecond side 108 b of the second die 102 b, and the individual firstconductive elements 122 are coupled to corresponding conductive traces114 (e.g., copper traces) on the first side 108 a of the first die 102a. The conductive traces 114, in turn, couple the individual TSVs 110 tothe integrated circuitry 103 of the semiconductor dies 102. Inadditional or alternate embodiments, the interconnect structures 120 canbe directly coupled to other types of conductive elements, such assubstrate pads or metal bumps. In practice, the semiconductor device 100can include a greater number of interconnect structures than shown inthe illustrated embodiments. For example, the semiconductor device caninclude four, eight, sixteen, fifty, a hundred, or more interconnectstructures disposed between each of the dies.

FIG. 2 is an enlarged cross-sectional view showing an individualinterconnect structure 220 in accordance with an embodiment of thepresent technology. As shown, the interconnect structure 220 includes afirst conductive element, or conductive pillar 222 (e.g., a copperpillar), and a second conductive element, or bond pad 223 (e.g., acopper pad), coupled to the conductive pillar 222 by an intermetallicpalladium joint 225 (“intermetallic joint 225”). In the illustratedembodiment of FIG. 2, the intermetallic joint 225 defines a bond linethickness t_(B) between the conductive pillar 222 and the bond pad 223.In the illustrated embodiment of FIG. 2, the intermetallic joint 225includes a plurality of intermetallic features 226 a-d (e.g.,crystallites) that each have a first end portion 221 directly bonded toa first barrier material 234 (e.g., a nickel-based material) on theconductive pillar 222, and they also have a second end portion directlybonded to a second barrier material 237 (e.g., a nickel-based material)on the bond pad 223. In the example shown in FIG. 2 the first and secondend portions 221 a-b define the bond line thickness t_(B) of the joint225. In at least some embodiments, the bond line thickness t_(B) can bein a range of from about 5 μm to 10 μm (e.g., about 7 μm). As describedin greater detail below, the intermetallic features 226 a-d havecorresponding volumes Va-Vd, respectively, that are each composed ofpalladium and/or a palladium intermetallic material.

One challenge with conventional solder joints is that they can break(e.g. crack) depending on the relative concentration of the conductivematerials within the joint. For example, a large concentration ofunreacted metal solder can cause the joint to be too ductile, while alarge concentration of unreacted barrier material can cause the joint tobe too brittle. Palladium has been regarded in the semiconductor deviceindustry as a less favorable intermetallic material because conventionalsolder joints having significant concentrations of palladium orpalladium intermetallic materials are prone to breakage. Incontravention to this conventional understanding, however, it isbelieved that the palladium-based intermetallic features of the variousembodiments of the present technology increase the bond strength of aconductive joint. In particular, it is believed that the palladium-basedintermetallic features increase bond strength when they span the entirewidth of the joint. As described in greater detail below, it is alsobelieved that reliable conductive joints can be formed bythermo-compression bonding using selected amounts of metal solder andpalladium source material having as-deposited thicknesses that fallwithin selected ranges of thickness.

FIGS. 3A-3G are cross-sectional views illustrating a semiconductordevice 300 at various stages in a method for making interconnectstructures or other connectors in accordance with selected embodimentsof the present technology. Referring first to FIG. 3A, semiconductordevice 300 has a first dielectric material 316 a (e.g., silicon oxide)on the first side 108 a of the substrate 106, and the conductive trace114 is buried within the first dielectric material 316 a. The firstdielectric material 316 a has a patterned opening 317 that exposes asurface 318 of the buried conductive trace 114 within the opening 317.The conductive pillar 222 is located on the trace 114, a firstconductive material 334 is located on a surface 311 of the conductivepillar 222, and a film of bond material 340 is located on a surface 331of the first conductive material 334. The first conductive material 334can comprise a barrier material such as nickel. The bond material 340can comprise, for example, metal solder, such as tin/silver solder. Inat least some embodiments, the conductive pillar 222, the firstconductive material 334, and the bond material 340 can be plated insequence onto the conductive trace 114 via electroplating and/orelectroless plating. In other embodiments, however, materials can bedeposited using other techniques. For example, in one embodiment, thebond material 340 can be disposed on the surface 331 of the firstconductive material 334 in the form of a solder ball. In one aspect ofthis embodiment described in greater detail below, the bond material 340can be selected to have a suitable bond material thickness t_(S) thatfalls within a selected range to form suitable intermetallic featureswithin the intermetallic joint 225 (FIG. 2).

FIG. 3B shows the semiconductor device 300 after forming the bond pad223 on a corresponding TSV 110 in the substrate 106 of the firstsemiconductor die 102 a. The TSV 110 can be formed by first etching thesubstrate 106 at the second side 108 b to form an opening 362 thatextends from the second side 108 b to a substrate pad 365 located at thebase of the opening 362 and then filling the opening 362 with aconductive material 366 (e.g., copper or copper alloy). In an alternateembodiment, the TSVs 110 can be formed at a different processing stagesuch as before the processing stage shown in FIG. 3A (e.g., beforefront-end metallization). In at least some embodiments, the substrate106 can be thinned before forming the individual TSVs 110. The bond pad223 can be formed by depositing (e.g., plating) a conductive material336 (e.g., copper) onto a surface 363 of the TSV 110. In the illustratedembodiment, the bond pad 223 can be electrically insulated from thesubstrate 106 by a second dielectric layer 316 b formed between the bondpad 223 and the substrate 106 at the second side 108 b.

FIG. 3C shows the semiconductor device 300 after forming a secondconductive material 337 on the bond pad 223 and a film of palladiummaterial 342 on a surface 339 of the second conductive material 337. Thesecond conductive material 337 can comprise a barrier material, such asnickel. In one embodiment, the second conductive material 337 and thepalladium material 342 can be deposited in sequence onto the bond pad223 (e.g., via electroplating and/or plating). As described in greaterdetail below, the palladium material 342 is formed to have a palladiumthickness t_(P) that falls within a selected range to form suitableintermetallic features within the intermetallic joint 225 (FIG. 2).

In at least some embodiments, the palladium material 342 can be formedto have a surface 345 containing a plurality of heterogeneous nucleationsites 347. The nucleation sites 347 can include, for example,topographical features, lattice discontinuities/orientations, surfacedefects, textures, and/or other surface features. As described ingreater below, the nucleation sites can seed the growth of theintermetallic features during thermo-compression bonding. In additionalor alternate embodiments, the second conductive material 337 can also beconfigured to have features (e.g., surface features, latticediscontinuities, etc.) that lead to the formation of suitable nucleationsites at the surface 345 and/or below the surface 345.

FIGS. 3D-3F show the semiconductor device 300 at selected stages ofthermo-compression bonding. In general, thermo-compression bondingtechniques use a combination of heat and compression (e.g., z-axisand/or vertical force control) to form a conductive solder joint betweena pair of conductive materials. The combination of heat and compressionof the solder between the conductive materials produces a bondingreaction that is relatively faster than the bonding reaction oftraditional reflow techniques. For example, the overall processing timefor a thermo-compression bonding process is typically on the order of15-20 seconds. Another advantage of thermo-compression bonding is thatmetal solder is only allowed to flow for a limited amount of time beforeit cools and then hardens. As such, thermo-compression bonding canmitigate degradation that may otherwise occur due to migration of solderaway from the joint and consumption of conductive material at thesidewalls of a conductive feature (e.g., at the sidewalls of a copperpillar).

FIG. 3D shows the semiconductor device 300 at an initial stage ofthermo-compression bonding in which the bond material 340 has beenheated and the semiconductor dies 102 have been brought into proximatelywith one another. As shown, the palladium material 340 is contacting thebond material 340. FIG. 3E shows a subsequent bonding stage in which thesemiconductor dies 102 have been moved into closer proximity with oneanother relative to FIG. 3D. At the stage of FIG. 3E, the bond material340 has partially reacted with both the palladium material 342 and thesecond conductive material 337, which has initiated the growth of theintermetallic features 226 a-d at the nucleation sites 347 (FIG. 3D). Asshown, the growth of the intermetallic features 226 a-d is generallyanisotropic (vertically in FIG. 3E). As discussed above, the nucleationsites 347 (FIG. 3D) can include various surface features (e.g.,topographical features). It is believed that these surface features canbe configured to influence the growth of the intermetallic features 226a-d and thereby achieve, e.g., a certain size, distribution, and/ororientation of the intermetallic features within an intermetallic joint.

FIG. 3F shows the semiconductor device 300 after the semiconductor dies102 have been moved into closer proximity with one another relative toFIG. 3E. As shown, the intermetallic features 226 a-d have grown furtherin the vertical direction and have reacted with the first conductivematerial 334 on the conductive pillar 222. In at least some embodiments,the first conductive material 334 and/or the second conductive material337 can be fully converted into intermetallics during bondingthermo-compression bonding. Also, the bond material 340 can be fullyconverted into an intermetallic material during thermo-compressionbonding or at a subsequent thermal processing stage (e.g., an annealingstage or another bonding stage). For example, referring to FIG. 3G,subsequent thermal processing can convert residual bond material 340into an intermetallic material that defines the intermetallic features226 a-d.

As discussed above, the intermetallic features 226 a-d comprisepalladium and/or an intermetallic palladium based material (e.g.,palladium and nickel, palladium and tin, or palladium, nickel, and tin).As noted above, it is believed that suitable palladium-basedintermetallic features can be formed using thermo-compression bonding incombination with selected amounts of metal solder and palladium sourcematerials. For example, it is believed that reliable intermetallicfeatures can be formed when the initial palladium thickness t_(P) (FIG.3C) is in a range of from about 0.1 μm to 0.3 μm (e.g., about 0.15 μm to0.25 μm) and the initial bond material thickness t_(S) (FIG. 3A) is in arange of from about 5 μm to 15 μm (e.g., 10 μm). It is also believedthat suitable intermetallic features can be formed using other sourcematerials in lieu of palladium. For example, it is believed that a noblemetal, such as gold, may be used to form suitable gold-basedintermetallic features.

For purposes of comparison, FIGS. 4A and 4B show interconnect structures420 a and 420 b, respectively, having palladium intermetallic joints 425a and 425 b. In FIG. 4A, the intermetallic joint 425 a was formed viathermo-compression bonding in accordance with the present technologyusing a tin/solder bond material having an initial bond materialthickness t_(S) (FIG. 3A) of 10 μm and a palladium source materialhaving an initial palladium thickness t_(P) (FIG. 3C) of 0.15 μm. Theresulting intermetallic features 426 (enhanced for clarity) of the joint425 a in accordance with an embodiment of the present technology extendacross the entire bond line thickness. In FIG. 4B, by contrast, theintermetallic joint 425 b was formed via conventional thermo-compressionbonding technology using a greater initial thickness of solder andpalladium. As shown in FIG. 4B, the intermetallic joint 425 b contains alarge amount of unconverted bulk solder 427, and the intermetallicmaterial of the joint 425 b has failed to form a suitable bond betweenthe conductive pillar and the bond pad. In particular, the jointcontains a cracked region 429 (enhanced for clarity in FIG. 4B) suchthat the joint 425 b is defective.

Any one of the interconnect structures and/or semiconductor devicesdescribed above with reference to FIGS. 1-4A can be incorporated intoany of a myriad of larger and/or more complex systems, a representativeexample of which is system 590 shown schematically in FIG. 5. The system590 can include a semiconductor device 500, a power source 592, a driver594, a processor 596, and/or other subsystems or components 598. Thesemiconductor device 500 can include features generally similar to thoseof the semiconductor devices described above, and can therefore includevarious features that enhance heat dissipation. The resulting system 590can perform any of a wide variety of functions such as memory storage,data processing, and/or other suitable functions. Accordingly,representative systems 590 can include, without limitation, hand-helddevices (e.g., mobile phones, tablets, digital readers, and digitalaudio players), computers, vehicle and other machines and appliances.Components of the system 590 may be housed in a single unit ordistributed over multiple, interconnected units (e.g., through acommunications network). The components of the system 590 can alsoinclude remote devices and any of a wide variety of computer readablemedia.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustrationbut that various modifications may be made without deviating from thedisclosure. Moreover, although advantages associated with certainembodiments of the new technology have been described in the context ofthose embodiments, other embodiments may also exhibit such advantages,and not all embodiments need necessarily exhibit such advantages to fallwithin the scope of the technology. Accordingly, the disclosure andassociated technology can encompass other embodiments not expresslyshown or described herein.

I claim:
 1. An interconnect structure, comprising: a first conductiveelement; a second conductive element; and an intermetallic palladiumjoint defining a bond line thickness between the first and secondconductive elements, the intermetallic palladium joint comprising aplurality of intermetallic crystallites each having a first end portiondirectly coupled to the first conductive element, and a second endportion directly coupled to the second conductive element, wherein eachof the crystallites spans the entire bond line thickness, and whereineach of the crystallites is composed of intermetallic palladium.
 2. Theinterconnect structure of claim 1 wherein the bond line thickness is ina range between about 5 μm to 10 μm.
 3. The interconnect structure ofclaim 1, further comprising a first barrier material on the firstconductive element, the first barrier material bonding the first endportion of each of the crystallites to the first conductive element. 4.The interconnect structure of claim 3, further comprising a secondbarrier material on the second conductive element, the second barriermaterial bonding the second end portion of each of the crystallites tothe second conductive element.
 5. The interconnect structure of claim 4wherein each of the first and second barrier materials comprises nickel.6. The interconnect structure of claim 1 wherein the intermetallicpalladium joint further includes a bond material between individual onesof the crystallites.
 7. The interconnect structure of claim 1 whereineach of the first and second conductive elements comprises copper.
 8. Asemiconductor device, comprising: a first semiconductor die; a secondsemiconductor die adjacent the first semiconductor die; and a pluralityof interconnect structures between the first and second semiconductordies, wherein each of the interconnect structures includes— a firstconductive element, a second conductive element, and an intermetallicpalladium joint between the first conductive element and the secondconductive element, wherein the intermetallic joint includes a pluralityof intermetallic features that each form a conductive bond between thefirst conductive element and the second conductive element, wherein eachof the intermetallic features is composed of a discrete volume ofintermetallic palladium that forms a first end portion directly coupledto the first conductive element, and a second end portion directlycoupled to the second conductive element.
 9. The semiconductor device ofclaim 8 wherein each of the interconnect structures includes a firstnickel material bonding the first end portion of each of theintermetallic features to the first conductive element, and a secondnickel material bonding the second end portion of each of theintermetallic features to the second conductive element.
 10. Thesemiconductor device of claim 8 wherein each of the interconnectstructures further includes a tin material between individual ones ofthe intermetallic features.
 11. The semiconductor device of claim 8wherein at least one of the first and second conductive elementscomprises a bond pad.
 12. The semiconductor device of claim 8 wherein atleast one of the first and second conductive elements comprises aconductive trace.
 13. The semiconductor device of claim 8 wherein atleast one of the first and second conductive elements comprises aconductive pillar.
 14. The semiconductor device of claim 8 wherein atleast one of the first and second semiconductor dies is a memory die.15. The semiconductor device of claim 8 wherein at least one of thefirst and second semiconductor dies is a logic die.